Brain regional μ-opioid receptor function in rat lines selected for differences in alcohol preference

Abstract It has been suggested that opioid peptides play a role in the reinforcing effects of alcohol. The present study was designed to examine the function of the μ-opioid receptor system in rat lines selectively bred for alcohol preference (AA [Alko, Alcohol] rat line) and alcohol avoidance (ANA [Alko, Non-Alcohol] rat line). The functional coupling of μ-opioid receptors to G proteins was determined autoradiographically using Tyr- d -Ala-Gly-N(Me)Phe-Gly-ol-enkephalin-stimulated [ 35 S]GTPγS binding in brain cryostat sections. The binding was significantly increased in the striatal patches and substantia nigra reticulata of the AA rats in comparison with that of the ANA rats. Within the AA rat line, there was a significant positive correlation between 3 mg/kg morphine-induced locomotor activity and activation of G-proteins in the substantia nigra compacta and nucleus accumbens core. These results of the selective breeding experiment suggest that brain region-specific differences in μ-opioid receptor function may correlate with innate differences in alcohol preference.